1. Field of Invention
The present invention relates to the field of motor vehicle safety and concerns a hybrid gas generator unit.
2. Description of Related Art
In recent years, new generators called adaptive generators have appeared, for limiting the risk of body injuries brought about by deployment of the airbag. To do this, these various generators, coupled to suitable detection systems, allow the flow rate and/or the volume of gas to be modulated according to certain parameters such as, for example, the morphology and the position of the passenger, the ambient temperature, and the nature and intensity of the impact. These generators are in all cases designed to operate within a time period of about fifty milliseconds.
Very recently, motor vehicle manufacturers wanted to incorporate devices using inflatable airbags to protect occupants, not only when the vehicle rolls over after a side impact. To do this, the airbags must remain inflated for some ten seconds. U.S. Pat. No. 5,967,550 discloses a generator provided with two pyrotechnic charges, the first serving to inflate the airbag within milliseconds after the accident and the second keeping the airbag inflated for some ten seconds. However, owing to the particular geometry of this generator, the latter cannot be easily integrated into all motor vehicles.
A device has therefore been proposed, as in patent application WO 01/34516, which comprises, on the one hand, a main body containing an electropyrotechnic igniter and a first pyrotechnic charge and, on the other hand, a tube attached to the main body and containing a second pyrotechnic charge consisting of powder particles. This device has the advantage, over the abovementioned generator, of possessing a compact main body coupled to a tube that can easily be housed along the vehicle""s roof. However, because of the use of two separate pyrotechnic charges, the cost of manufacturing such a device is relatively high, this being prejudicial in a competitive market such as that of the motor vehicle industry. In addition, the use of a pyrotechnic charge in the form of powder particles in the tube is detrimental since, in operation, very hot particles are in the airbag and these can cause premature degradation of the latter. Moreover, the use of a pyrotechnic charge to generate gas during a period of some ten seconds has the effect that the surface of the device is maintained at a temperature of about several hundred degrees Celsius over this time period. This may be damage for the airbag or the vehicle furnishings near the device.
A person skilled in the art is therefore always looking for a device for alleviating the abovementioned problems.
The subject of the present invention relates to a hybrid gas generator unit used for motor vehicle safety to inflate at least one side airbag, characterized in that it comprises:
a flexible element containing a pyrotechnic charge and having an upstream end and a downstream end;
a reservoir of pressurized gas, the said reservoir having an upstream end and a downstream end;
an electropyrotechnic igniter housed in a body located near the upstream end of the flexible element and the downstream end of the reservoir; and
the said igniter being capable during operation, on the one hand, of initiating the combustion of the pyrotechnic charge contained in the flexible element and, on the other hand, of causing the pressurized gas contained in the reservoir to be released.
This generator unit, apart from the fact that it possesses a geometry allowing it to be integrated into all kinds of motor vehicles, therefore has a greatly reduced manufacturing cost owing to the use of a pressurized gas reservoir instead of a pyrotechnic charge.
Preferably, the pyrotechnic charge contained in the flexible element is capable of generating a volume of gas sufficient to fully inflate the airbag in a time period of less than forty milliseconds. Moreover, in operation, the pressurized gas contained in the reservoir is released so as to keep the airbag inflated for a time period of the order of several seconds. This pressurized gas is uniformly released only from the moment when the airbag has been fully inflated after the combustion of the pyrotechnic charge.
Advantageously, the pyrotechnic charge contained in the flexible element is produced in the form of a cylindrical block which, on the one hand, preferably has a length very much greater than its diameter and, on the other hand, is provided with a central channel. Again, advantageously, this pyrotechnic charge consists of a composite propellant comprising a charge based on ammonium perchlorate, sodium nitrate and an inert binder.
Preferably, a heat-shrunk pliant sleeve grips and confines the pyrotechnic charge contained in the flexible element.
Advantageously, the electropyrotechnic igniter initiates, on the one hand, the combustion of the pyrotechnic charge contained in the flexible element and causes, on the other hand, the pressurized gas contained in the reservoir to be released by means of booster charges.
Preferably, the upstream end of the flexible element and the downstream end of the reservoir are attached to a ring which is itself fastened in the body.
Also preferably, this device is designed so that, after combustion of the pyrotechnique charge, the gas escapes from the reservoir in order to pass through the body and then leaves in a substantially opposite direction in order to pass through the flexible element.
Again, advantageously, the flexible element is produced using a pliant tube made of a thermoplastic, provided with outlet orifices uniformly distributed over its circumference and along its length. Since the pyrotechnic charge is housed in the tube, all that is therefore required is to adapt the length of this tube to the size of the airbag used. In addition, the choice of such a material to form the tube makes the generator unit safer since, in the event of abnormal pressurization, any spraying of metal parts liable to injure an occupant is prevented.